Liquid crystal displays are used in a wide variety of commercial applications including portable (laptop) computers, wristwatches, camcorders and large screen televisions. Liquid crystal light valves, used as spatial light modulators, may be used in projection systems as well as optical computing applications. Limitations inherent in the existing technology come from the necessity of fabricating the displays on transparent glass or quartz substrates which are not amenable to high quality electronic materials. Fabrication of displays on bulk silicon, although of high crystal quality, unnecessarily constrains the display to reflective mode schemes due to the opaque substrate and is not applicable to transmissive applications. The ability to integrate drive circuitry using thin-film transistors (TFTs) with liquid crystal displays has improved reliability and has allowed the use of this technology in lightweight, portable applications. However, the integration of display driving circuitry heretofore has been substantially limited to thin film transistor technology using amorphous (a-Si) or polycrystalline (p-Si) silicon deposited on the glass or quartz substrate.The intrinsic properties such as lattice and thermal mismatch between the silicon layer and the substrate, and the low temperature deposition techniques used in the a-Si and p-Si technologies result in a silicon layer with poor charge carrier mobility and crystallographic defects. These limitations are directly related to inferior electronic device performance and limitations when compared to bulk silicon.
Of particular importance for integrated display systems is the desire for higher density circuitry for ultra-high resolution display and light valve applications and for the monolithic integration of display driver circuitry and related signal processing circuitry on-chip. The characteristic lower (electrical and crystallographic) qualities of a-Si and p-Si materials result in poor fabrication yields when compared to conventional Very Large Scale Integration (VLSI) processing. Overcoming this problem, inherent in the poorer quality amorphous or polycrystalline material, requires the use of redundant circuit elements in each pixel to ensure fully functional displays in a-Si and p-Si. This redundancy requires an concomitant increase in the picture element (pixel) size thereby inhibiting the ability to scale displays and light valves to ultra-high resolution. The additional circuit elements also reduce the aperture ratio, i.e. the fraction of pixel area allowing transmitted light, thereby reducing the brightness of the display or light valve.
Furthermore, the low carrier mobility, low speed, low yield a-Si and p-Si materials are incompatible with VLSI design and fabrication techniques which would otherwise readily allow integration of video drivers, digital logic and other computational circuitry on-chip thereby offering designers greater functionality, higher reliability, and improved performance.
Thus, a need has been recognized for an electrically addressable ultra-high resolution nematic liquid crystal display or light valve system which monolithically integrates an active matrix display with its associated drive and image processing circuitry.
The present invention is directed to an ultra-high resolution liquid crystal display that includes liquid crystals and integrated control circuitry formed from a thinned layer of single crystal silicon. The liquid crystal display includes: a) a sapphire substrate having a first crystal lattice structure; b) a single crystal silicon structure having a thickness no greater than about 100 nanometers affixed to the sapphire substrate to create a silicon-on-sapphire structure, and a second crystal lattice structure oriented by the first crystal lattice structure; c) an array of liquid crystal capacitors formed on the silicon-on-sapphire structure; and d) integrated circuitry formed from the silicon layer which is operably coupled to modulate the liquid crystal capacitors. The liquid crystals capacitors may include nematic or ferroelectric liquid crystal material.
The thinned layer of single crystal silicon supports the fabrication of device quality circuitry on the silicon-on-sapphire structure which is used to control the operation of the pixels that may be individually addressed to create an image. The types of liquid crystal capacitors that may be fabricated in conjunction with the invention may be ferroelectric liquid crystal capacitors and nematic liquid crystal capacitors.